Generator Collapse with a Falling Carboxyhaemoglobin and a Normal Saturation

Yes - several independent criteria are met.

Accepted indications in carbon monoxide poisoning include any history of loss of consciousness, persisting neurological abnormality, cardiac ischaemia or arrhythmia, metabolic acidosis, and a COHb above roughly 25% (some services use 20%). This man has:

• Loss of consciousness of about 15 minutes plus prolonged confusion and incontinence - neurological involvement, which is the strongest predictor of delayed neurological sequelae.
• ST depression in the lateral leads with a troponin above the upper reference limit - myocardial injury from tissue hypoxia; this is an indication in its own right and also a risk factor for arrhythmia during treatment.
• Lactate 3.1 mmol/L - a marker of significant tissue hypoxia and acidosis, and of severity.

Why the numbers are misleading

• COHb 24% sounds low, but it was drawn 90 minutes after removal. The half-life on room air is roughly 4–5 hours, so the peak value was substantially higher; the level has already fallen while the tissue injury persists.
• A smoker has a baseline COHb of around 5–10%, so the exposure-related increment is smaller than it looks, but severity is judged on clinical findings, not on the level.
• SpO2 is normal because standard pulse oximetry cannot distinguish carboxyhaemoglobin from oxyhaemoglobin; a 99% reading is expected and is not reassurance.

Timing: treatment should start as soon as practicable; benefit is greatest within the first 6 hours, but delayed treatment still reduces delayed neurological sequelae, so a 3-hour transfer is not futile.

Facility choice

• The monoplace unit is 45 minutes away but unstaffed until 08:00. A 5-hour wait is unacceptable for a patient with neurological and cardiac involvement.
• The patient is not stable enough for a monoplace chamber as a first choice: he has ongoing myocardial ischaemia and needs continuous cardiac monitoring, IV access, airway support if his GCS falls, and an inside attendant who can intervene. Most monoplace chambers cannot provide an attendant, and the patient must lie still and tolerate the hood or mask alone.
• Therefore activate the 24-hour multiplace chamber, but ask the monoplace unit to call in staff as a contingency: if it can be staffed and the attending physician agrees the patient is stable enough, a treatment there at 2.5–3.0 ATA followed by transfer is better than 3 hours of untreated travel. Base the decision on staffed capability, not distance.

Plan for the interval

• 100% oxygen continuously by a tight-fitting mask with reservoir, or a demand valve; do not interrupt it for transport handovers. Record that the mask was properly sealed.
• Continuous cardiac monitoring and 12-lead ECG on arrival and after any chest pain; serial troponin; treat ischaemia medically; avoid hypotension and hypoxia.
• IV access, glucose, lactate and blood gas; consider elective intubation before transfer if GCS drops or vomiting is uncontrolled.
• Alert the receiving chamber with the history, the troponin, the ECG findings and the estimated arrival time; confirm an attendant and monitoring are available.
• Avoid exertion and smoking; the patient should not walk to the ambulance.

Remaining risks

• Delayed neurological sequelae occur in roughly 10–30% of significant poisonings, typically 2–40 days later, with cognitive slowing, personality change, gait disturbance or incontinence. Risk is higher with age over 40, loss of consciousness, acidosis and prolonged exposure - he has three of these.
• Myocardial injury: an elevated troponin with ischaemic ECG changes means he needs serial troponins and an echocardiogram; arrhythmia risk persists after COHb normalises, because the injury is to the myocardium, not the haemoglobin.
• Recurrence of exposure: the generator must not be used again indoors, and his home should be assessed.

Advice

• Do not drive himself, and do not drive until cleared - cognitive slowing and the risk of arrhythmia make him unsafe; arrange a lift.
• Follow-up at 4–6 weeks with neuropsychological testing and a repeat clinical examination, and tell him to return immediately for confusion, memory problems, unsteadiness, mood change or incontinence. Those symptoms warrant further hyperbaric treatments, which are effective for delayed sequelae.
• Cardiologist review with echocardiography and consideration of ambulatory monitoring.
• Smoking cessation advice, and written safety guidance about generators and carbon monoxide detectors.
• Document that he was warned about delayed effects, since the asymptomatic period is when patients stop attending follow-up.